python tips

1. enum

Python code

#!/usr/bin/env python
# -*- coding:utf-8 -*-

def enum(**enums):
    return type('Enum', (), enums)
Gender = enum(MALE=0,FEMALE=1)
print Gender.MALE
print Gender.FEMALE

2. Check whether the string is a number

Python code

s='123456789'
s.isdigit()#return True

3. List intersection

Python code

s=[1,2,3]
w=[2,3,4]
list(set(s).intersection(w))

4. Two lists Convert to a dict

Python code

dict(zip(a,b))

5, singleton

Python code

def singleton(cls):
    instances = {}
    def get_instance():
        if cls not in instances:
            instances[cls] = cls()
        return instances[cls]
    return get_instance

The second singleton mode used in tornado IOLoop:

Python code

@staticmethod
def instance():
    """Returns a global IOLoop instance.

    Most single-threaded applications have a single, global IOLoop.
    Use this method instead of passing around IOLoop instances
    throughout your code.

    A common pattern for classes that depend on IOLoops is to use
    a default argument to enable programs with multiple IOLoops
    but not require the argument for simpler applications::

        class MyClass(object):
            def __init__(self, io_loop=None):
                self.io_loop = io_loop or IOLoop.instance()
    """
    if not hasattr(IOLoop, "_instance"):
        with IOLoop._instance_lock:
            if not hasattr(IOLoop, "_instance"):
                # New instance after double check
                IOLoop._instance = IOLoop()
    return IOLoop._instance

6.list Duplication removal

Python code

{}.fromkeys(list).keys()